Field
The present invention relates generally to voltage regulation for Integrated Circuit technology, and more specifically to efficient noise immune voltage regulation in Integrated Circuits requiring.
Background
A voltage regulator is designed to automatically maintain a constant voltage level. A voltage regulator may be a simple “feed-forward” design or may include negative feedback control loops. It may use an electromechanical mechanism or electronic components. Depending on the design, it may be used to regulate one or more Alternating Current (AC) or Direct Current (DC) voltages. Electronic voltage regulators are found in devices such as computer power supplies where they stabilize DC voltages used by the processor and other elements. The stability of the output voltage can be significantly increased by using an operational amplifier. The operational amplifier drives its transistor with more current if the voltage at its inverting input drops below the output of the voltage reference at a non-inverting input. A voltage divider allows selection of an arbitrary output voltage.
Traditional apparatus and methods for electronic operational amplifier voltage regulation in Integrated Circuits (ICs) typically require physical separation between analog and digital circuit blocks as well as individual external bypass capacitors for each voltage regulation node requiring an individual external pin interface. These external bypass capacitors at the output of the integrators quiet the regulated voltage node by filtering noise from the power supply signal line.
A linear power line regulator may also step a higher voltage down to a lower voltage used as a power supply for specific digital hardware blocks, traditionally in conjunction with a an external capacitor to filter environmental noise. However, an external capacitor for each internal voltage regulation node necessitates an external pin on the Integrated Circuit package for each internal regulation node of the IC, generating size and complexity issues as well as additional manufacturing costs. For example, in implementations having multiple digital and analog functional blocks requiring ten internal regulation nodes, an additional ten external pins and associated capacitors must be added to the IC package. Due to noise in the environment, many voltage regulators are inefficiently required in order to quiet the analog blocks, requiring more and more regulators and their associated external pins and capacitors coupled to ground.
Unfortunately, such external bypass capacitors create inductances between the internal node, the capacitor and the Printed Circuit Board (PCB) substrate generating concomitant parasitic signals that impair performance of high frequency circuits. The external capacitor effectively filters noise and parasitics at low frequencies but not at high frequencies because those components that are introduced through the IC package and the PCB substrate inherently reduce the efficiency of the capacitor. Above certain frequencies, the quality factor is reduced because of the components in series with the capacitor, which can no longer effectively filter noise and parasitic signals from the environment. In other words, an ideal capacitor with no parasitic signals around it has a linear transfer function. It attenuates at a frequency N. Attenuation increases linearly with increase in frequency. If no additional components are introduced around the capacitor, the transfer function remains linear. Adding resistors or other components in series with the capacitor causes the transfer function to become non-linear as it reaches a threshold operational frequency, flattening out the transfer function and degrading the ability of the capacitor to filter parasitic noise. At higher frequencies, the capacitor loses its efficiency and no longer acts as a filter. Many of the functional hardware blocks beneficially protected by voltage regulation are operating at high frequencies, traditionally forcing physical IC separation of analog and digital blocks, separate ground planes and implementation of External Power Management Integrated Circuit (PMIC) devices.
Complexity and manufacturing costs drive an ever increasing need for integration of functionality and analog and digital hardware blocks in ICs, which requires an internal solution capable of guaranteeing enough noise immunity for high frequency analog sensitive blocks to reside within an IC device without being contaminated by noise from other hardware blocks. Inversely, noise generated by these other blocks must be contained within those blocks.
There is therefore a need in the art for noise immune voltage regulation at high frequencies suitable for SOC implementation without the need for individual external bypass capacitors, their associated performance degradation, and multitude of external interface pins on the IC package, while also providing enough gain for operation.